This project addresses mechanisms leading to increased coronary artery related deaths in post-menopausal women. We hypothesize ovarian steroid hormones (SH) regulate vascular reactivity by modulation of thromboxane A2 (TxA2) receptors, increased expression of which may explain the hyperreactive element of coronary vasospasm. Previously, we established a reliable, non-injury model in the rhesus monkey of extreme, prolonged focal constrictions relevant to human coronary vasospasm. The key to inducing hyperreactivity that allows these focal constrictions in response to the platelet release products, serotonin and thromboxane A2 , is elimination of ovarian steroid hormones. We plan to further study the basis for this major primate regulatory influence by exploring the receptor mechanisms. These studies employ controlled levels of treatment for 2 weeks with androgen (A), estrogen (E), and/or progesterone (P), and will differentially explore contributions of each SH to coronary reactivity. Physiological levels of E and P will be used to better define conditions permitting the protected state (prevention of prolonged focal constrictions and myocardial ischemia during challenges with serotonin and TxA2) of coronary artery reactivity. Ovariectomized monkeys >11 years old will be studied using coronary catheterization at the Dotter Institute radiology laboratory, followed by isolation of coronary artery vascular muscle cells (VMC) to measure Ca2+ and protein kinase C (PKC) signal alterations which may explain long-duration contractions underlying vasospasm. Measurements will be made of thromboxane A2 receptors by radio-labeled ligand binding and immunocytochemistry. Pathological investigations of coronary arteries will evaluate the role of structural occlusions or artery injury in increased reactivity. VMC in optimized primary cell culture (in non-proliferating conditions retaining membrane characteristics, contraction, and reactivity to vasoconstrictors) will be used to study the basis for the modulation of reactivity, exploring transformations between states of normal and exaggerated reactivity. The major mechanism by which SH provide protection appears to be via modulation of the VMC TxA2 receptor. Thus, TxA2 receptors will be studied as possible causes of vasospasm, as modulated by A, E, and P. These experiments are designed to determine how SH modulate vascular muscle cell reactivity in order to better understand how SH can be used to minimize the probability of coronary vasospasm.